In the electrical wiring and related industries and arts, a tube is used to protect and route electrical wiring in a building or structure. This tube is called electrical conduit. Electrical conduit may be made of many types of materials and commonly is made of metal, plastic, fiber, or fired clay. Most commonly conduit is rigid and inflexible. Electricians and those of skills in the electrical arts at the site of installation of electrical equipment typically install conduit. The installation of conduit is labor intensive and requires each individual piece of conduit to be threaded to joining devices called a coupling. The threaded coupling and conduit are then threaded to another piece of conduit and coupling. This process is then repeated until a specific length of coupling is joined together to facilitate the passage of wiring through the conduit. The use, form, and installation details of conduit are often specified by wiring regulations, such as the US National Electrical Code (NEC) and other building codes.
The origins of early electric lighting installations trace the use of existing gas pipe serving gas light fixtures which had been converted to electric lamps. Since this technique provided very good mechanical protection for interior wiring, it was extended to all types of interior wiring and by the early 20th century purpose-built couplings and fittings were manufactured for use in the electrical arts. The electrical wiring arts evolved and electrical codes now prohibit the routing of electrical conductors through gas piping due to concerns about causing damage to electrical insulation from the rough interiors of pipes and fittings that are used for gas.
Electrical conduit provides very good protection to enclosed conductors from impact, moisture, and chemical vapors. Electrical conduit has varying numbers, sizes, and allows different types of wiring to be pulled into the conduit. This simplifies the design and construction when comparing it to requiring multiple runs of cables. In addition, because wiring systems in buildings may be changed over the course of time, conduit allows the ease of changing wiring. Conduit also makes changing wiring simpler and safer as existing conductors can be withdrawn and new conductors installed, with little disruption along the path of the conduit.
A layout of conduit can be made waterproof or submersible. The use of metal conduit can shield sensitive circuits from electromagnetic interference. The use of metal conduit can also prevent emission of such interference from enclosed power cables. In addition, conduit will not permit the flow of flammable gases and vapors with seal offs. This result provides protection from fire and explosion hazard in areas handling volatile substances.
In the construction of structures, there is a need to encase conduit in concrete and certain types of conduit are approved for this use. Encasement in this manner is typically used in commercial buildings to allow electrical and communication outlets to be installed in the middle of large open areas.
Some types of metal conduit may also serve as a useful bonding conductor for grounding. Some wiring regulations may also dictate standards or supplemental means of grounding for certain types of conduit.
Conduits must be installed by electricians following standard regulations, as those provided by the National Electrical Code (NEC).
Electrical conduit is called Galvanized Rigid Conduit or Rigid Metal Conduit (RMC). A conduit made from galvanized steel tubing is commonly referred as a rigid conduit. The thickness of a galvanized rigid conduit protects the electrical wiring from being hit and allows it to be threaded. Galvanized rigid conduits are used by electricians in commercial and industrial applications normally available in 10 foot and 20 foot lengths and may be used in shorter lengths as necessary and available or through the process of cutting and placing threads on the shortened conduit.
Rigid Metal Conduit (RMC) and Rigid Steel Conduit (RSC) are the heaviest and thickest types of conduit. They are typically made of coated steel, stainless steel, red brass or aluminum. These pipes can be installed above ground or underground. The threads on the uncoupled end of the pipes are covered by industry color-coded thread protectors, which protect the threads, keeping them clean and sharp.
RMCs and RSCs are generally corrosive resistant and optionally come with a layer of PVC or zinc added to areas that are wet or highly corrosive. The zinc coating provides extra coating in areas that are wet, or highly corrosive. Galvanized Rigid Conduit (GRC) are created by taking RMC, RSC, or IMC and galvanizing it via hot dipping it in zinc.
Aluminum is also used and is cheaper than a galvanized rigid conduit and lighter than a GRC conduit. Intermediate metal conduit (IMC) is steel tubing heavier than EMT but lighter than RMC.
Rigid electrical conduit is also available as Electrical Metallic Tubing (EMT). An EMT conduit is made of steel. Electrical metallic tubing (EMT), sometimes called thin-wall, is commonly used instead of galvanized rigid conduit (GRC), as it is less costly and lighter than GRC. Lengths of conduit are connected to each other and to equipment with clamp-type fittings. Like GRC, EMT is more common in commercial and industrial buildings than in residential applications. EMT is generally made of coated steel, though it may be aluminum. EMT is also a very popular material in commercial and industrial buildings because it can be bent to specific radius and directions and it is thinner than RMC.